NOTES
March, 1958
379
pumping for one hour at 100". Into a cold finger containing 4.6 mmoles of this labeled salt were then distilled 1.62 mmoles of Sic&, using liquid N t summary as a refrigerant, Since HC136, formed by the Both sodium and carbonate ions have previously hydrolysis of Sic14 by any traces of moisture still been shown t o be incorporated in the surface of remaining in the tetramethylammonium chloride, hydroxy apatite crystals by ion exchange processes. would simulate exchange (especially in exchange Because, in bone in vivo, these two ions appear to be runs between labeled SiC14 and unlabeled salt, see related, an attempt was made to test whether any below) the cold finger was momentarily warmed t o specific interaction between sodium and carbonate O o , then cooled with acetone-Dry Ice slush, and ions occurs at the hydroxy apatite surface in vitro. subjected to high vacuum pumping t o remove Carbonate ions did increase incorporation by any HC1 present. The cold finger was warmed to apatite of both sodium and potassium ions but the 0" and aliquots of Sic& removed at known time effects were small and non-specific. The associa- intervals, radioassayed and returned to the reaction between sodium and carbonate ions in bone is, tion cold finger. The counting technique for the therefore, probably the result of physiological assay of volatile labeled materials has been demechanisms, scribed in detail.6 The activity observed in the
therefore, be the result of physiological mechanisms mentioned earlier.
ISOTOPIC EXCHANGE REACTIONS. 11. THE RAPID HALOGEN EXCHANGE BETWEEN Sicla AND (CH&NCl, AND A CONVENIENT METHOD FOR THE PREPARA-
TION OF
c 1 3 6
LABELED CHLOROSILANES
BY ROLFEH. HERBER Department of Chemistry and Chemical Engineering, University of Illinois, Urbana, Ill. Received November I , 1867
In a detailed study1 of the halogen exchange kinetics in the system SiC13nC136-HCln (in which n denotes the natural isotopic composition) it was pointed out that isotopically labeled silicon tetrachloride could be prepared by a homogeneous gas phase exchange with HC136. The reaction halftimes for reactant concentrations of mole per liter were found to be on the order of lo4 seconds at 90". Since, under these conditions the total quantity of SiC14which can be labeled in a given run is small, we have looked for a more suitable exchange path. Schomaker and Stevenson2 have suggested that the difference beiween the sum of the covalent bond radii (2.16 A.) and, the observed interatomic distance in Sic14 (2.02 A.) is due to partial ionic bond character contributions of the type SiC18+C1-. As Lewis and Wilkins3 have shown in the case of NOC1, such ionization should lead to rapid exchange with appropriate ionized solutes and hence we have explored the exchange between (CH&NCl and Sic14 since the former is known to ionize readily in a number of non-aqueous solvent^.^ In a typical exchange run, Cla6-labeled(CH3)4NC1 was prepared by dissolving the reagent grade salt in a minimal volume of water, adding one drop of HC136stock solution5 and evaporating off the water and HC1 under high vacuum conditions. The resulting solid was subjected to high vacuum (1) R. H.Herber, J . Chem. Phys., 27, 653 (1957). (2) V. Schomaker and D. P. Stevenson, J . Am. Chem, Soc., 68, 37 (1941). (3) J. Lewis and R. G. Wilkins, J. Chem. SOC.,56 (1955). (4) A. B. Burg and D. E. McKenzie, J . Am. Chem. Soc., 74, 3143 (1952): V. Gutmann, Z.anow. allgem. Chem.. 266, 331 (1951). (5) Item C1-36-P, Oak Ridge National Laboratory, Isotopes Divi-
sion.
Me,,NCI-S!CI:
AT 30.C.
MINUTES.
Fig. 1.-Activity of silicon tetrachloride.
silicon tetrachloride as a function of time is shown in Fig. 1. In a second experiment, SiC14and labeled (CH3)4NC1maintained for 3 hours at 50°, resulted in an activity of 220 c.p.m./cm. SiCL. We have also noted the reverse exchange in which labeled silicon tetrachloride with an initial specific activity of 200 c.p.m./cm. was contacted with unlabeled (CHs)4NCla at room temperature. The observed c.p.m./cm. were 182 for 5 minutes, 129 after 10 minutes, 77.3 after 20 minutes and 70.7 after 30 minutes. Calculation of the fraction of total exchange, based on the observed "infinite time" activity, appears to indicate that the exchange may proceed via a heterogeneous mechanism. A further experiment in which (CHa)3SiC1nwas substituted for the tetrachloro species indicates that this material, too, exchanges halogens at room temperature with (CH3)4NC136. The use -of high specific activity tetramethylammonium chloride thus provides a conyenient starting point for the preparation of chlorine labeled SiC1, and (CH3)3SiC1 and the exchangeis noted to be reasonably rapid at room temperature. Due to the condensed nature of this system, relatively large quantities of labeled product can be prepared in a single exchange run. This research has been supported in part by the U. S. Atomic Energy Commission. The assistance of Mr. W. Cordes in this work is gratefully acknowledged. (6) R . H. Herber Paper #24, 132nd Meeting Am. Chem. SOC., New York City, 1957; R. H. Herber. Rev. 9ci. Inst., in press.
